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Chemistry AS > Halogenoalkanes > Flashcards

Halogenoalkanes Flashcards

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1
Q

General formula of halogenoalkanes

A

CnH2n+1X (X = halogen)

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2
Q

What prefixes tell us what halogen is present?

A

fluoro-
chloro-
iodo-

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3
Q

What prefixes tell us how many atoms of each halogen are present?

A

di-
tri-
tetra-

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4
Q

How is compound named when containing different halogens?

A

Listed in alphabetical order, not in order of the number of carbon atoms to which they are bonded

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5
Q

Is the C–X bond polar?

A

Yes

C (delta +)
X (delta -)

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6
Q

What happens to polarity of bond going down the group?

A

Gets less polar

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7
Q

Are halogenoalkanes soluble in water?

A

No

C–X bonds aren’t polar enough to make them soluble in water

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8
Q

What are the main intermolecular forces in halogenoalkanes?

A

dipole-dipole attractions and van Der Waal forces

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9
Q

What uses can there be when halogenoalkanes mix with hydrocarbons?

A

Can be used as dry-cleaning fluids and to remove oily stains

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10
Q

The boiling point _______ with _______ chain length

A

The boiling point INCREASES with INCREASED chain length

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11
Q

The boiling point _______ going _______ the halogen group

A

The boiling point INCREASES going DOWN the halogen group

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12
Q

Why does boiling point increase with:

  • Increased chain length
  • Going down the halogen group
A

Increased van Der Waals forces because the larger molecules, the greater the number of electrons

Therefore, the larger the van Der Waals forces

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13
Q

What is the difference of boiling points between halogenoalkanes and alkanes (with similar chain lengths)?

Why?

A

Halogenoalkanes have HIGHER boiling points than alkanes with similar chain lengths

They have higher relative molecular masses and they are more polar

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14
Q

What are the two factors that determine how readily the C–X bond reacts?
Which is more important?

A

C–X bond polarity

C–X bond enthalpy (more important)

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15
Q

The carbon bonded to the halogen has a partial positive charge. It is electron _______

A

It is electron deficient

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16
Q

Definition of nucleophiles

A

Species that has a lone pair of electrons with which it can form a covalent bond by donating its electrons to an electron deficient carbon atom

(positive charge loving) - attracted to positively charges species

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17
Q

Is C–F or C–I most or least reactive?

Why?

A

C–F most reactive - most polar therefore more likely to be attacked by a nucleophile

C–I least reactive - least polar

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18
Q

The bonds get _______ going down the group

A

The bonds get WEAKER going down the group

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19
Q

Why is C–F a strong bond?

A

Fluorine is smallest atom

Shared electrons in C–F bond are strongly attracted the fluorine nucleus

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20
Q

Why does the C–X bond get weaker going down group 7?

A

Shared electrons in the C–X bond get further away from halogen nucleus

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21
Q

What charge does a nucleophile have?

In what form?

A

Negative

Either negatively charged ion or has an atom with delta - charge

22
Q

What does a nucleophile contain?

What does this form?

A

Lone pair of electrons

Used to form a covalent bond

23
Q

What are the common nucleophiles?

How should they be written?

A 
Hydroxide ion (OH-)
Ammonia (NH3)
Cyanide ion (CN-)

(have to be shown with lone pair and -, except NH3, no -)

24
Q

What can nucleophilic substitution be used to produce?

A

Alcohols and amines

25
Q

What does the lower curly arrow show?

What does the halogen atom become?

A

The electron pair in the C–X moving to the halogen atom (X)

A halide ion (leaving group)

26
Q

What is the leaving group in nucleophilic substitution?

A

The halide ion

27
Q

What does the rate of substitution depend on?

Example:

A

The halogen

Fluoro-compounds unreactive due to strength of C–F bond

28
Q

Going down the group, the rate of reaction _______ as the C–X bond strength _______

A

Going down the group, the rate of reaction INCREASES as the C–X bond strength DECREASES

29
Q

Conditions for -OH nucleophile (aqueous sodium or potassium hydroxide)

A
  • Warm the mixture (slow at room temp)

- Ethanol as a solvent (so halogenoalkanes and aqueous sodium or potassium hydroxide both mix - hydrolysis reaction)

30
Q

Condition for -CN nucleophile (cyanide ions)

A

In ethanol

31
Q

Conditions for NH3 nucleophile

A
  • In ethanol
  • Heat in sealed tube
  • Carried out under pressure
32
Q

What nucleophile (+ halogenoalkanes) produce alcohol?

A

OH- (H20)

33
Q

What nucleophile (+ halogenoalkanes) produce nitrile?

A

CN- (KCN or NaCN)

34
Q

What nucleophile (+ halogenoalkanes) produce amine?

A

NH3 (concentrated NH3)

35
Q

Definition of elimination reaction?

A

A reaction in which a molecule loses atoms or groups of atoms to form a double C bond

36
Q

Product of an elimination reaction

A

Alkene (hydrogen halide eliminated leaving double bond in its place)

37
Q

What is OH- in an elimination reaction (under different conditions than in nucleophilic substitution)?

What does it do?

A

Acts as a base

Removed an H+ ion from halogenoalkane

38
Q

What conditions needed for elimination reaction with OH- (sodium/potassium hydroxide)?

A

Sodium/potassium hydroxide dissolved in ethanol and mixed with halogenoalkane

Mixture heated

39
Q

Would OH- at room temp, dissolved in water favour substitution or elimination?

A

Substitution

40
Q

Would OH- at high temp, dissolved in ethanol favour substitution or elimination?

A

Elimination

41
Q

Does elimination need ethanol or water as a solvent?

A

Ethanol

42
Q

Does substitution need ethanol or water as a solvent?

A

Water

43
Q

Does a high temperature encourage elimination or substitution?

A

Elimination

44
Q

Does a higher concentration encourage elimination or substitution?

A

Elimination

45
Q

Primary halogenoalkane - nucleophilic substitution or nucleophilic elimination?

A

Nucleophilic substitution

46
Q

Tertiary halogenoalkane - nucleophilic substitution or nucleophilic elimination?

A

Nucleophilic elimination

47
Q

What are chlorofluorocarbons (CFCs)?

A

Halogenoalkanes which only contain carbon, chlorine and fluorine - NO HYDROGEN

48
Q

What were the short chain CFCs (gases) used for?

A

E.g. Refrigerants

49
Q

What were the long chain CFCs used for?

A

Dry cleaning and de-greasing solvents

50
Q

What happens when CFC gases end up in the atmosphere?

A

They decompose to give chlorine atoms

Chlorine atoms decompose ozone (O3) in the stratosphere, which caused hole in Earths ozone layer

51
Q

What was the supposed benefits of CFCs?

A

Non toxic

Non flammability

52
Q

What has been developed instead of CFCs?

A

HCFCs - contain hydrogen

Decompose more easily than CFCs due to C–H bonds and chlorine atoms released lower in the atmosphere where they do not contribute to destruction of ozone layer

…and also HFCs - no chlorine

Therefore no damage to ozone layer

Chemistry AS (14 decks)

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